To increase the intensity of laser beams, there have been attempts made to perform, by using wavelength dispersive elements, wavelength coupling on a plurality of laser beams having different wavelengths emitted from a plurality of laser media. Performing “wavelength coupling” in this specification means causing a plurality of laser beams having different wavelengths to exit at the same exit angle, i.e., a plurality of laser beams having different wavelengths are superimposed on each other to form one laser beam.
Patent literature 1 discloses a technology in which an external resonator that includes a plurality of laser media and a wavelength dispersive element sets the wavelengths of the laser beams emitted from the laser media to a unique value and another wavelength dispersive element installed outside the external resonator couples the laser beams emitted from the laser media.